The invention relates to a phase shift amplifier comprising a first and a second transistor arranged to form a differential input pair supplied with steady current, these transistors each having a control electrode for receiving an input signal, and an output electrode, in which amplifier the output electrode of the first transistor is connected to a terminal of a first phase shift resistor and also to a terminal of a first phase shift capacitor, the output electrode of the second transistor is connected to a terminal of a second phase shift resistor and also to a terminal of a second phase shift capacitor, the second terminal of the first phase shift resistor is connected to the second terminal of the second phase shift capacitor at a first node, and the second terminal of the second phase shift resistor is connected to the second terminal of the first phase shift capacitor at a second node.
The invention likewise relates to a recombining circuit which effects for either one of the two differential input signals which are phase shifted relative to each other, an amplification and a summation of these signals after a complementary phase shift, one of the input signals presenting a first component of a given phase and the other input signal presenting a second component which has a quadrature phase relationship to the first component.
Phase shift amplifiers are used nowadays in numerous applications and, more particularly, in the field of radio frequency transmissions. A typical application consists of producing two signals which are quadrature signals in view of their transmission coding. A second particularly important example of the use of phase shift amplifiers with respect to reception comprises the realization of a mixer in which two phase shift amplifiers are used which allow, when the quadrature phase shift is ideally adhered to, the elimination of the image frequency in a superheterodyne receiver.
A phase shift amplifier of the type defined in the opening paragraph is known from document WO-A-9211704 where it is described more particularly with reference to FIG. 2 of that document. The known phase shift amplifier utilizes networks of the series arranged RC type connected in parallel between the output electrodes of the transistors of the input stage. This amplifier operates, in essence, with a voltage because circuits of phase shift resistors-phase shift capacitors produce at their junctions a signal in the form of an output voltage signal, so that a high input impedance should be used.
In effect, the impedance used affects the phase shift of the output signals when it is not large relative to the impedance of the elements of the RC network. This indicates a serious drawback from the point of view of current consumption. In effect, to maintain a high signal-to-noise ratio at the output of the phase shift amplifier, it is necessary to supply this amplifier with a relatively large current. But at the output of the phase shift amplifier, a power amplifier is necessary which is also to be supplied with a large current for the same reason.